When you are on a company ground; canteen, apron, changing room etc...it is still a company who owns or rents that place therefore you are to obey their regulations. "English only" is mostly to show the respect to other people not talking your native language as If you would put yourself in the middle of Rwanda and listen to Swahili, kinnda weird right?
So don't get to emotional with this,the English is the most spoken language amidst the international crews anywhere...so this doesn't come as a surprise.